SLS or ovine hereditary chondrodysplasia is a genetic disorder causing skeletal deformities in young lambs. These defects commonly include abnormally long and bent limbs, twisted spines, shallow bodies, flattened rib cages, and long necks. The syndrome is inherited as a genetic recessive disorder, meaning that affected lambs must inherit the mutation from both their parents. Because of this inheritance pattern, the identification of genetic carriers of SLS has been difficult without the use of progeny testing. The presence of SLS in several breeds has prompted breeders to divide pedigrees into two categories: "gray-pedigreed" animals having ancestors that have produced spider lambs, and "white-pedigreed" animals having ancestors that have never produced affected lambs.

There is a DNA test that can be used to help identify carriers as well as animals that are free of SLS. Since its development, the DNA test has been validated in thousands of animals. To date, it has been 100% accurate in the proper identification of animals that are genetically free or carriers of this defect. The test has been successfully used in Suffolks, Hampshires, Southdowns, and Oxfords.